1. Field of the Invention
The present invention relates to a watertight slide fastener and, more particularly, to a watertight slide fastener preventing leakage through a top end stop thereof.
2. Description of the Related Art
FIG. 1 shows a conventional slide fastener 8 including a pair of fastener tapes 81. Scoops 82 are disposed on two mutually facing edges of the fastener tapes 81. A resilient top end stop 83 is mounted on the fastener tapes 81 and is connected to the scoops 82. The resilient top end stop 83 includes an accommodating portion 84 in a central portion thereof for accommodating a stud 86 of a slider 85. A protrusion 87 extends upright along a periphery of the resilient top end stop 83. A passage portion 88 is defined in an entrance of the resilient top end stop 83. Flanges 89 of the slider 85 press against two outer edges of the resilient top end stop 83 to sealingly close the passage portion 88. An example similar to the conventional slide fastener 8 is disclosed in JP Publication No. 4-36659. In the conventional slide fastener 8, the sealing closure of the passage portion 88 merely relies on the pressure against the two outer edges of the resilient top end stop 83 by the flanges 89 of the slider 85. In a case that the force pressing against the two outer edges of the resilient top end stop 83 is insufficient, leakage is apt to occur at the passage portion 88.
FIG. 2 shows another conventional slide fastener 9 designed to improve the above leakage problem. The conventional slide fastener 9 also includes a pair of fastener tapes 91, scoops 92 disposed on two mutually facing edges of the fastener tapes 91, and a resilient top end stop 93 separate from the scoops 92. The resilient top end stop 93 includes an accommodating portion 94 for accommodating a stud 96 of a slider 95. A protrusion 97 extends upright along a periphery of the resilient top end stop 93. A passage portion 98 is defined in an entrance of the resilient top end stop 93. A pair of pressing portions 99 is disposed on outer edges of the resilient top end stop 93 and corresponds to the passage portion 98. The resilient top end stop 93 and the pressing portions 99 can be pressed by flanges 90 of the slider 95 to sealingly close the passage portion 98, attaining better impermeability to water and air. An example similar to the conventional slide fastener 9 is disclosed in U.S. Pat. No. 7,591,051 B2 (Taiwan Patent Publication No. 200716008) entitled “WATERPROOF TOP END STOP OF SLIDE FASTENER.”
The resilient top end stop 93 is made of an elastic, soft material, and slider 95 is made of a rigid material such as zinc alloy or hardened plastic material added with fillings (such as fiberglass, fibers, etc.). The transverse dimension of the resilient top end stop 93 is larger than that of the interior of the flanges 90 of the slider 95. For example, a #10 slide fastener generally has a tolerance of 10% in the dimension. Thus, a larger lateral force imparted to the flanges 90 of the slider 95 is required to press against the resilient top end stop 93 and the pressing portions 99 for sealingly closing the passage portion 98 of the resilient top end stop 93, thereby attaining impermeability to water and air. Nevertheless, the resilient top end stop 93 made of the resilient material will generate an interfering force resisting the compression. In this case, pulling the slider 95 for opening or closing the scoops 92 becomes difficult and needs a larger force. Furthermore, after a period of time of repetitious use of the slide fastener 9, the resilient top end stop 93 made of soft material becomes worn due to repeated rubbing by the slider 95, adversely affecting the sealing closure of the passage portion 98 and failing to attain the impermeability to water and air.
Thus, improvement to the conventional slide fasteners is necessary.